1. Field of the Invention
The field of the invention relates to fluid dispensing mechanisms and, more particularly, to an improved dispensing apparatus which may be miniaturized and which is capable of delivering precisely controlled quantities of fluid.
2. Brief Description of the Prior Art
There are a number of known designs for dispensing fluids such as adhesives, sealants, and the like at accurately controlled flow rates, in accurate quantities, and for accurate placement on a receiving surface.
In certain designs, fluid is introduced under pressure to a reservoir and dispensed upon movement of a valve member off a valve seat. U.S. Pat. Nos. 4,930,669 and 4,955,514 disclose two such designs. Each design is sealless, which is highly advantageous for dispensing fluids which tend to leak through and/or destroy conventional seals.
Another type of dispensing apparatus is disclosed in U.S. Pat. No. 4,858,789. This design allows the positive displacement of precise quantities of fluid from a reservoir. All three patented devices discussed above employ a deformable diaphragm for isolating the reservoir from the mechanism which actuates the valve, thereby preventing the undesirable entry of product into the mechanism.
Other types of dispensers are disclosed in U.S. Pat. Nos. 4,066,188, 4,066,845, 4,099,653 and 4,126,321. The first three patented dispensers are designed primarily for dispensing hot, viscous fluids, while the latter is designed for use as a spray gun. Each employs a bellows seal for isolating a fluid reservoir from an actuating mechanism.
U.S. Pat. No. 3,871,558 discloses an apparatus for dispensing viscous products such as liquid soap via positive displacement. The products are confined by a bellows-type membrane.
There are many different types of fluids which require the use of a dispensing apparatus. Such fluids have a very broad range of viscosities, curing properties, and other characteristics which may preclude the use of certain types of dispensers. Cyanoacrylates, for example, of relatively low viscosities tend to diffuse with polymers and then cure. These properties make the use of dynamic seals in a dispenser very disadvantageous. If high pressure within the fluid reservoir is required, diaphragm seals become disadvantageous as the pressure against such seals must be overcome in order to move the stem or slide to which the valve member is secured.
Fluid dispensers may also be used in a wide variety of applications, some of which require incorporation of the dispenser within sophisticated machinery. Others may require the ability to manipulate the dispenser manually. The ability to manufacture a dispenser which is small in size and easily manipulated by hand is important in many applications. As the fluid reservoirs of many dispensers are supplied with fluid through fittings in the reservoir walls, the dispensers are rather difficult to handle as the fittings and associated tubing are obstructions which must be avoided.
The ability to miniaturize existing dispenser designs is often limited due to the manner in which fluid is supplied to the reservoir, as described above. Other internal structures in many dispensers also severely limit the extent to which they can be miniaturized. As small size and light weight are advantageous features in a number of applications, many prior art dispensers are of only limited utility.